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Fresh water pump blues

Discussion in 'Technical Discussion' started by Danvilletim, Aug 11, 2015.

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  1. Danvilletim, Aug 11, 2015
    #1
    Danvilletim

    Danvilletim Senior Member

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    I could use some input in chasing down a problem.. We have two 4hp Ac water pumps ( one for backup) that power the fresh water for 62 Striker. They have been cycling on and off a lot and we expected either a leak or accumulator tank at 4 gallons is too small.

    Today we found a leak in the plumbing assembly coming out of the tank to the pumps and went to replace them. We noticed that old assembly's had a check value. Is this usual?

    After new assembly was installed with new check values, one pump can't build up enough pressure to hit the 50 PSI cut off threshold. even when the selector value is off only allowing two feet of hose in front of the pump?

    Any ideas or comments?
  2. wdrzal, Aug 11, 2015
    #2
    wdrzal

    wdrzal Senior Member

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    With out the check valve as soon as the pump shuts off the water in the accumulator tank would backflow through the pump back into the holding tank . There are several reasons why it won't build pressure, a picture of the pump would help lot in diagnoses. 4 hp sounds like a lot to me if its just used to supply fresh water from a holding tank. 1/3to 1/2 hp unless therein a lot more to the fresh water system than described.
  3. Capt J, Aug 11, 2015
    #3
    Capt J

    Capt J Senior Member

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    4hp sounds like a lot to me too. It sounds like you have an air leak on the suction side. Check the plumbing to the pump that's not building enough pressure.
  4. Danvilletim, Aug 11, 2015
    #4
    Danvilletim

    Danvilletim Senior Member

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    The previous owner over built everything. Air leak on suction side seems reasonable idea. Perhaps the new check value was bad. Or we had too many leaks in the new assembly.

    Is a 4 gal accumulator tank sufficient for 3 stateroom, 4 bath?
  5. wdrzal, Aug 11, 2015
    #5
    wdrzal

    wdrzal Senior Member

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    If you have a bladder type pressure tank, the pre-charge air pressure is also critical, the tank installation manual will tell you what the pre-charge tank pressure should be if you want a 50 psi pump off pressure . Normally a 20 psi differential pressure is recommended (on @ 30 psi off, @ 50 psi). I use a 10 to 12 psi differential,20 psi is way to noticeable if in the shower. Is it large enough???? a smaller tank will just make the pump pressure switch cycle more often, the contacts will probably fail a litter sooner due to more on and off cycles ,but pressure switches are cheap and even with a smaller tank they will last a long time.
  6. Capt Ralph, Aug 11, 2015
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    I'm hoping that's 1/4 hp pump. 4 hp will never get a chance to run or charge correctly. Probably making it's own air / aerating the water.

    4 gal accumulator is good sized and would usually work fine an a boat with less than a 1/2 hp pump.
    Not for a 4 hp pump.
  7. CSkipR, Aug 19, 2015
    #7
    CSkipR

    CSkipR Member

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    Agree that 1/2 or 3/4 is plenty for a fresh water system in that size vessel and a 4 gal accumulator should also be plenty. Does the pump or pressure switch have an adjustment to increase/decrease pressure? Does each pump have its own accumulator or are they plumbed together? Posting a picture of the pump and setup would sure help.
  8. Danvilletim, Aug 22, 2015
    #8
    Danvilletim

    Danvilletim Senior Member

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    After two attempts the suction side is now leak free and pump is no longer cycling. Still need to test how many seconds of faucet run time I get before pump cycles back on.